Heretofore, a PZT (PbTO3-PbZrO3) constituent-based ceramic containing lead has been used in a piezoelectric ceramic composition. The reason for it is that the aforesaid PZT, exhibiting excellent piezoelectric properties and a high mechanical quality coefficient, can readily produce materials exhibiting various desired characteristics which are required for various applications such as a sensor, an actuator, and a filter. Further, since the PZT has a high relative dielectric constant, it may also be used as a capacitor.
However, while the piezoelectric ceramic composition composed of the aforesaid PZT exhibits excellent characteristics, it contains lead as an element constituting the composition, leading to a concern that toxic lead is eluted off from industrial waste of products containing PZT to result in an environmental pollution. The increasing awareness of environmental issues in recent years has made it difficult to manufacture the products containing substances such as PZT which have been a cause of environmental pollution. To cope with the above problem, piezoelectric ceramic compositions have been developed which include no lead in their compositions and whose primary component is a chemical compound which is represented by formula {LiX(K1-YNaY)1-X}(Nb1-Z-WTaZSbW)O3, wherein x, y, z and w are within the ranges of 0≦x≦0.2, 0≦y≦1, 0<z≦0.4, and 0<w≦0.2, respectively (refer to Patent Document 1).
A polarization method has been disclosed in which the first step where a piezoelectric ceramic composition, exhibiting a cubic crystal structure at a high temperature and a reversible phase transition to tetragonal and then to orthorhombic structures when the temperature decreased, is subjected to the first polarization processing, and the second step where the above piezoelectric ceramic composition is subjected to the second polarization processing in a temperature range in which the composition exhibits an orthorhombic structure and in the same direction of polarization as the above first polarization processing are provided in the piezoelectric ceramic composition in which the primary component described above exhibits a perovskite structure of ABO3 type to stably increase and saturate the polarization degree (refer to Patent Document 2).
Further, patent document 3 discloses a liquid droplet ejection head utilizing a piezoelectric actuator whose primary component is a piezoelectric ceramic composition having a perovskite crystal structure and including no lead. It also discloses that the above primary component includes barium titanate, potassium niobate, sodium bismuth titanate, bismuth nickel titanate, Ba2NaNb5O15, and Bi4Ti3O12.
Patent Document 1: Japanese Patent Application Publication (hereinafter also referred to as JP-A) No. 2004-300012
Patent Document 2: JP-A No. 2005-228865
Patent Document 3: JP-A No. 2005-246656